Gardening is an activity that has more than its share of techniques that fall in the “It’s always been done this way, so that’s how I’m going to do it” category. It’s not surprising; we are governed by nature to a large extent and our gardening chores have an obvious seasonal flavour to them.
Now that pruning time has arrived this topic has arisen again. Should pruning cuts be sealed to prevent infection? I had a short discussion with a customer in our garden centre about this last week and as soon as it was over I knew I had a topic for further discussion.
The answer to the question is no. Plants have a remarkable ability to heal themselves after a pruning cut has been made. The same process is at work after wind or ice storms. Plants naturally contain cells which go to work after the wound occurs. These cells seal off the wound and then the plant, in a process called compartmentalization, begins to fight off any potential infections. Think of it as built-in antibiotics.
To get a visual picture of this process at work take a close look at the trunk of a tree which has been properly pruned. You will see a ring of bark around the pruning cut that is different in appearance to the surrounding bark. This ring begins to form as soon as the cut is made and continues to build over time, producing a barrier to infections.
But, it only forms if the proper cut has been made and this is where gardeners can create problems for plants. Cut too far away from the trunk of the tree, or a bud on a branch of a shrub and you’ll be left with a stub that will die back to the point of the live bud below. Cut too close and the bud will dry up. In the case of the tree a cut too close to the branch collar will inhibit the formation of the cells which form that protective ring and infection may be able to move in.
The product known as “pruning paint” is asphalt. Asphalt is great for sealing cracks in your driveway but does it do anything for protecting a pruning cut on a tree or shrub? No, nature has figured that one out for us already. Pruning paint doesn’t harm the plant but it is not necessary.
Some believe that applying pruning paint will prevent sap from running from a branch after the cut. This isn’t true either. The sap that oozes from a pruning cut on a warm afternoon may not look like it’s running very fast but the pressure is certainly great enough that after a few days it will break through that solid asphalt glob on the end of the branch.
Enjoy your time pruning in the garden over the next few weeks. It can be an enjoyable interlude trimming and training last year’s growth before this year’s activity begins. Save the asphalt for your driveway however.